Projection image display

ABSTRACT

A projection display system includes: two light sources ( 102, 105 ); a condenser ( 103, 106 ) for condensing the light from the light sources; a time-division color separating optical system ( 108 ) for temporally switching the incident light into a first, second, or third color of light to be emitted; a light valve ( 118 ) capable of modulating the incident light individually for each pixel; a lighting optical system ( 111, 112, 114 ) for directing the light from the time-division color separating optical system onto the light valve, and a projection optical system ( 123 ) for magnifying and projecting a pixel on the light valve. The light from the two light sources ( 102, 105 ) is condensed on the time-division color separating optical system or its vicinity by the condenser ( 103, 106 ), and then superimposed. This can provide a projection display system that performs time-division driving and can achieve high-brightness projection images without increasing the size and cost of a system.

TECHNICAL FIELD First Invention

The present first invention relates to a projection display system thatdisplays images by driving one light valve in response to light signalsthat present different colors temporally (time-division driving).

Second Invention

The present second invention relates to a projection display system thatmagnifies and projects images generated by a reflection-type light valvewithout relying on a polarizing beam splitter (hereinafter, referred toas PBS).

BACKGROUND ART First Invention

The market for large-scale image display systems that are used primarilyfor presentation is growing rapidly today. A wide range of applications,from portable displays to extremely large screens used in halls or thelike, is included in this market. The common requirements to be met bythe individual display systems for such applications are highbrightness, low cost, and miniaturization. There are two types ofprojection display systems: three-plate and single-plate. Thethree-plate type is provided with light valves, one each for R (red), G(green), and B (blue). The single-plate type is provided with one lightvalve for displaying color images. To meet the above-describedrequirements, in particular, to achieve cost reduction, the projectiondisplay systems of the single-plate type have been used increasingly inrecent years.

The single-plate type also can be classified broadly into two systems:one is a system using a light valve provided with pixels correspondingto each of the RGB colors; the other is a system using a light valvethat displays images by changing modulation factors temporally inresponse to each of the RGB signals with the same pixel.

The first system can have a simple configuration. However, the qualityof projection images is poor, strictly speaking, as the RGB in thoseimages are displaced. On the other hand, the second system can providegood image quality without displacement of the RGB. However, itsconfiguration is more complex than the first system.

The present invention is intended to improve the second system.

Hereinafter, the second system, i.e., a single-plate display systememploying time-division driving, will be described. In this displaysystem, a light valve is driven at a speed that is three times as fastas the conventional one in response to each of the input signals of RBG.It is necessary that the incident light on the light valve also beswitched correspondingly.

A lighting system that illuminates a subject by switching white lightsequentially to the RBG colors of light is disclosed in, e.g., JP2-119005 A. FIG. 7 shows a schematic configuration of the lightingsystem. The light from a light source 301, which emits white light,passes through a condenser lens 302 and a color wheel 303 into theincident end of a light guide 304. Then, the light is projected onto asubject for observation from the exit end of the light guide. In thiscase, the color wheel 303 is a rotating disk formed of three fan-shapedfilters. The three filters are as follows: a red-transmission filter forpassing only light in the wavelength range of red, a green-transmissionfilter for passing only light in the wavelength range of green, and ablue-transmission filter for passing only light in the wavelength rangeof blue. The color wheel 303 is rotated by a motor 305. The rotation ofthe color wheel 303 allows the subject to be illuminated with red,green, and blue light that is switched sequentially.

The above lighting system is applied to a projection display system,which is disclosed in, e.g., JP 9-185902 A. FIG. 8 shows a schematicconfiguration of the projection display system. The light emitted from alight source 401 is reflected from a reflecting mirror 402 toward theopening thereof. Then, only visible light is reflected from a reflectingmirror 403 provided with a filter for rejecting ultraviolet and infraredrays, and its optical path is deflected by 90 degrees. The reflectedvisible light passes through a brightness-modulation filter 405 andcolor-modulation filters 404 a, 404 b, and 404 c in this order, so thatthe entire brightness of the light is modulated. Then, the light entersa color wheel 406. The color wheel 406 is provided with a tri-colorfilter including: a filter for passing only light in the wavelengthrange of red; a filter for passing only light in the wavelength range ofgreen, and a filter for passing only light in the wavelength range ofblue. By rotating the color wheel 406, the color of the light passingthrough the color wheel can be selected sequentially. The transmittedlight is collimated by a condenser lens 407 into parallel light,reflected from a mirror 408, and enters a projection gate 409. Then, thelight is modulated and emitted from the projection gate 409 and directedthrough a relay lens 410 and a stop 411 to a projection lens 412. Thus,an image on the projection gate 409 is magnified and projected onto ascreen (not shown). At this time, a color signal that drives theprojection gate 409 and a color of the light passing through the colorwheel 406 are synchronized, so that modulation can be performed inaccordance with a color of the light entering the projection gate 409.This makes it possible to display color images with a single lightvalve. In the above configuration, the light from the light source 401is condensed on the color wheel 406 or its vicinity. This is because thesize of the color wheel 406 is reduced and a period of color mixture isminimized; the color mixture occurs when the incident light on the colorwheel 406 passes through two different adjacent color selecting filtersat the same time.

As described above, when a rotating color wheel is used fortime-division driving, it is preferable that an image of the lightsource is small, which is condensed and formed on a color selectingfilter of the color wheel or its vicinity. On the other hand, since thetime-division driving basically reduces the optical output of a systemto one-third, a light source that can provide high brightness isnecessary. However, a discharge tube is used generally as the lightsource of a projection display system. Therefore, to achieve highbrightness as well as practical lifetime, the distance betweenelectrodes is increased and a light-emitting portion becomes large. Whensuch a light source with high-brightness and a large light-emittingportion is used, the image of the light source that is condensed andformed on a color selecting filter of the color wheel or its vicinityalso becomes large. This causes an increase in the size of the rotatingcolor wheel, the degradation of projection images because of colormixture, or the like.

Thus, for a conventional projection display system that performstime-division driving with a rotating color wheel, it has been difficultto achieve high brightness.

Second Invention

The market for large-scale image display systems that are used primarilyfor presentation is growing rapidly today. A wide range of applications,from portable displays to extremely large screens used in halls or thelike, is included in this market. The common requirements to be met bythe individual display systems for such applications are highbrightness, high resolution, low cost, and miniaturization. It should gowithout saying that the selection of a light source suitable for eachdevice size and the optimization of optical systems are needed tosatisfy these requirements.

Hereinafter, an example of a configuration of a conventional projectiondisplay system employing a reflection-type light valve will bedescribed.

A first conventional technique that is disclosed in JP 5-150213 A willbe described. As shown in FIG. 19, among the light from a light source701, the light reflected from a reflector 702 passes through apolarizing plate 703 and enters a reflection-type liquid crystal panel704. The reflection-type liquid crystal panel 704 modulates the incidentpolarized light to image light corresponding to an image to be displayedand reflects it diagonally. The reflected light passes through thepolarizing plate 703 again and is projected onto a screen 705 by aprojection lens 706. Thus, an image on the reflection-type liquidcrystal panel 704 can be magnified and projected onto the screen.

Before JP 5-150213 A was published, a configuration including areflection-type liquid crystal panel was such that a polarizing beamsplitter (PBS) is arranged near the reflection-type liquid crystalpanel. However, JP 5-150213 A has achieved the improvement in contrastand the reduction in cost by removing a PBS.

Next, a second conventional technique will be described, in which imagesare displayed by modulating the emission angle of the incident lightwithout depending on polarization, like an AMA reflection-type lightvalve, introduced at the ASIA DISPLAY '95. FIG. 20 shows a configurationdisclosed in U.S. Pat. No. 5,150,205. The light 801 emitted from a lightsource (not shown) is reflected from reflecting surfaces 802 providedfor each pixel in a reflection-type light valve. The reflecting surfaces802 can be inclined individually at different angles. For displayingwhite, the reflecting surface 802 is not inclined, so that the lightincident on this surface passes through an aperture 804 in a stop 803,then reaches a projection lens 805, and is magnified and projected. Onthe other hand, for displaying black, the reflecting surface 802 isinclined at predetermined angles, so that the light incident on thissurface is blocked by the stop 803. Therefore, the light does not passthrough the aperture 804 in the stop 803 to the projection lens 805,resulting in a black portion on a screen. In this configuration, apolarizer and analyzer made of an organic material are not used, andthus the structure is simple.

FIG. 21 shows a third conventional technique employing a similarreflection-type light valve. A projection display system according tothis technique includes a light source 901, a lighting optical system902, a schlieren optical system 903, a reflection-type light valve 904,and a projection optical system 905. The light from the light source 901is incident on schlieren bars 906 through the lighting optical system902. The light reflected from the schlieren bars passes through aschlieren lens 907 into the reflection-type light valve 904. Thereflection-type light valve 904 is provided with many reflectingmirrors, each of which is the same as that shown in FIG. 20. Since themirror arranged at the portion to be displayed in black reflects theincident light back to its path, the light thus reflected returns to theoptical path on the light source side through the schlieren lens 907 andthe schlieren bars 906 again. On the other hand, the mirror arranged atthe portion to be displayed in white is inclined with respect to theincident light. Therefore, the incident light is reflected in thedirection that is different from its path. The reflected light thusdeflected is focused by the schlieren lens 907 to form an image on thesurface of the schlieren bar 906. However, the imaging position isbetween the bars, so that the light can pass through here. Thetransmitted light enters the projection optical system 905. Thus, animage on the reflection-type light valve 904 can be magnified andprojected. In this configuration, the light source conditions can bemade without depending directly on the emission angle (the amount ofmodulation) of the light entering the reflection-type light valve 904.

However, each of the conventional projection display systems describedabove has the following problems.

Referring to the first configuration (shown in FIG. 19), when the angleof incidence of the light entering the reflection-type light valve 704is large, contrast cannot be maintained because of the dependence on theincidence angle when a liquid crystal is used as a reflection-type lightvalve 704. Moreover, when the angle between the optical axis of thelight reflected from the reflection-type light valve 704 and the opticalaxis of the projection optical system is large, an image is projected ata large elevation angle. Thus, the position where a projection image isdisplayed is limited practically. For these reasons, it is preferred toreduce the angle of incidence of the light entering the reflection-typelight valve.

Furthermore, when the interference between the light incident on andreflected from the reflection-type light valve 704 is caused, or can becaused, structural difficulties arise in forming a system. Thus, likethe above, it is necessary to reduce the angle of incidence of the lightentering the reflection-type light valve.

However, to reduce the angle of incidence, it is required to increasethe degree to which the light entering the reflection-type light valvefrom the lighting optical system is collimated. To increase such adegree, i.e., to increase a lighting F number, a light source having asmall light-emitting portion should be used. Even if a light sourcehaving a large light-emitting portion is used, it cannot be utilizedefficiently. Therefore, the light source to be used is limited to adischarge tube-type lamp with a short arc, so that it is difficult toprovide sufficiently bright images.

In the second configuration (shown in FIG. 20), a reflection-type lightvalve displays images by modulating the emission angle of the incidentlight without depending on polarization. Like the first configurationdescribed above, when the interference between the light incident on andreflected from the reflection-type light valve is caused, or can becaused, structural difficulties arise in forming a system. Thus, it isnecessary to reduce the angle of incidence of the light entering thereflection-type light valve.

In addition to this, if the reflecting surfaces provided in thereflection-type light valve are inclined at sufficiently large anglesupon modulation, there is no problem. However, the inclination angle isextremely small, i.e., 5 degrees, according to the above document. Inthis case, half of the angle of divergence of the incident light shouldbe not more than 5 degrees. Thus, like the first configuration, a largerlighting F number is necessary, so that a light source is limited,resulting in insufficient brightness.

In the third configuration (shown in FIG. 21), like the secondconfiguration, a reflection-type light valve displays images bymodulating the emission angle of the incident light. Here, a schlierenoptical system is used, so that a lighting F number is not limited bythe inclination angle of the respective reflecting surfaces in thereflection-type light valve. However, to transmit light without losses,it is necessary to design a schlieren lens while taking into account theinclination angle of the respective reflecting surfaces. This means thatthe F number of the schlieren lens is lowered, which increases the setsize and the cost.

SUMMARY OF THE INVENTION First Invention

It is an object of the present first invention to solve the aboveconventional problems and provide a projection display system thatperforms time-division driving and achieves a high-brightness projectionimage without increasing the size and cost of a system.

To achieve the above object, the present first invention has thefollowing configuration.

A projection display system of the present first invention includes: alight source; a condenser for condensing the light from the lightsource; a time-division color separating optical system for temporallyswitching the incident light to a first, second, or third color of lightto be emitted; a light valve capable of modulating the incident lightindividually for each pixel; a lighting optical system for directing thelight from the time-division color separating optical system onto thelight valve, and a projection optical system for magnifying andprojecting a pixel on the light valve. The number of the light sourceand the condenser is two, respectively. The light from the light sourcesis condensed on the time-division color separating optical system or itsvicinity by the condensers, and both condensing positions aresuperimposed.

In this configuration, the light from the two light sources is condensedon the time-division color separating optical system or its vicinity toform images of the light sources, respectively, and the two light sourceimages are superimposed. Therefore, the light from the light sources canbe doubled while keeping the condensed and superimposed images of thelight sources small. Thus, a projection image with high brightness canbe achieved. Also, it is not necessary to provide a large-sizedtime-division color separating optical system, so that an increase inthe size of a system can be prevented and a rise in the cost can besuppressed as well. In addition, since the small superimposed images ofthe light sources are formed in the vicinity of the time-division colorseparating optical system, the degradation of images caused by colormixture can be prevented.

In the above configuration, the condenser may be an umbrella-typereflector provided with an elliptical reflecting surface. Alternatively,the condenser may include an umbrella-type reflector provided with aparabolic reflecting surface and optical components having a convex-lenseffect.

Furthermore, in the above configuration, it is preferable that thelighting optical system includes a lens for collimating the light fromthe time-division color separating optical system into substantiallyparallel light and an integrated optical system; the integrated opticalsystem includes a first lens array that divides the incident light intoseparate rays of light to form secondary images of the light source anda second lens array provided with a plurality of microlenses arranged atthe positions where the secondary images of the light source are formed.The use of the integrated optical system in the lighting optical systemallows for the improvement of utilization efficiency of the light fromthe light sources and the uniform luminance distribution in a projectionimage.

In the above configuration, the light valve may be a reflection-typelight valve. In this case, it is preferable that the shape of an exitpupil formed in the lighting optical system, which can be taken as alight-emitting surface when the lighting optical system is viewed fromthe reflection-type light valve, is such that the size in the directionparallel to a plane containing the axes of the light incident on andreflected from the reflection-type light valve is smaller than that inthe direction perpendicular to that plane, and that the followingrelationship is established:

F1>1/(2 sin (θ1/2))

F2<1/(2 sin (θ1/2))

where, among a lighting F number relative to the reflection-type lightvalve, F1 represents the lighting F number in the direction parallel tothe plane containing the axes of the light incident on and reflectedfrom the reflection-type light valve, F2 represents the lighting Fnumber in the direction perpendicular to that plane, and θ1 representsthe angle between the light incident on the reflection-type light valveand the light reflected from the reflection-type light valve into theprojection optical system.

This preferred configuration can improve the efficiency of condensinglight on the reflection-type light valve, resulting in high efficiencyand high brightness. Moreover, the degree of freedom in light sourcearrangement is increased, which facilitates the design of a system.

In the above configuration, a reflection-type light valve that cancontrol the polarization directions of incident light individually foreach pixel may be used as the reflection-type light valve describedabove. Moreover, a polarizer may be provided on an optical axis on theincident side of the reflection-type light valve and an analyzer may beprovided on an optical axis on the exit side thereof. Alternatively, areflection-type light valve provided with reflecting surfaces whoseinclination angle can be controlled individually for each pixel may beused as the reflection-type light valve described above. Moreover, thereflection-type light valve may display an image in such a manner thatthe inclination angle of the respective reflecting surfaces iscontrolled so as to change the emission angle of light, and therebylight to be incident on the projection optical system is selected foreach pixel.

Furthermore, it is preferable that the lighting optical system includesa lens for collimating the light from the time-division color separatingoptical system into substantially parallel light and an integratedoptical system; the integrated optical system includes a first lensarray that divides the incident light into separate rays of light toform secondary images of the light source and a second lens arrayprovided with a plurality of microlenses arranged at the positions wherethe secondary images of the light source are formed; and the entireshape of the second lens array is such that the size in the directionparallel to a plane containing the axes of the light incident on andreflected from the reflection-type light valve is smaller than that inthe direction perpendicular to that plane. This preferred configurationcan increase efficiency, brightness, and the freedom degree in thesystem structure.

Furthermore, it is preferable that a plane containing a system axis andthe two light sources is perpendicular to a plane containing the axes ofthe light incident on and reflected from the reflection-type lightvalve. This preferred configuration can reduce the size of a system inthe direction parallel to the plane containing the axes of the lightincident on and reflected from the reflection-type light valve.

Furthermore, it is possible that the time-division color separatingoptical system is a rotating color wheel having a light selecting meansthat is placed on the circumference of a circle whose center is thecenter of rotation of the color wheel and separates the incident whitelight into a first, second, or third color of light to be emitted. Thiscan provide a simple, low-cost, and highly efficient color selection.

Second Invention

It is an object of the present second invention to solve the aboveconventional problems and provide a projection display system that canincrease the freedom degree in the above optical limitations resultingfrom the use of a reflection-type light valve, specifically in the Fnumber setting for lighting and projection systems, and that can beoptimized in accordance with different applications. In particular, thepresent invention has an object of achieving high-brightness projectionimages and a highly efficient system in such a manner that a lighting Fnumber relative to a reflection-type light valve is reduced, and thusthe light from a light source having a large light-emitting portion canbe condensed.

To achieve the above objects, the present second invention has thefollowing configuration.

A first configuration of a projection display system of the presentsecond invention includes: a light source; a lighting optical system forcondensing the light from the light source on the desired position; areflection-type light valve capable of modulating the light from thelighting optical system individually for each pixel, and a projectionoptical system for magnifying and projecting a pixel on thereflection-type light valve. The shape of an exit pupil formed in thelighting optical system, which can be taken as a light-emitting surfacewhen the lighting optical system is viewed from the reflection-typelight valve, is such that the size in the direction parallel to a planecontaining the axes of the light incident on and reflected from thereflection-type light valve is smaller than that in the directionperpendicular to that plane. Furthermore, the following relationship isestablished:

F1>1/(2 sin (θ1/2))

F2<1/(2 sin (θ1/2))

where, among a lighting F number relative to the reflection-type lightvalve, F1 represents the lighting F number in the direction parallel tothe plane containing the axes of the light incident on and reflectedfrom the reflection-type light valve, F2 represents the lighting Fnumber in the direction perpendicular to that plane, and θ1 representsthe angle between the light incident on the reflection-type light valveand the light reflected from the reflection-type light valve into theprojection optical system.

As described above, the appearance of a light-emitting portion in thelighting optical system when viewed from the reflection-type lightvalve, i.e., a lighting F number, is optimized in two directions; one isparallel to a plane formed by the light incident on and reflected fromthe reflection-type light valve and the other is perpendicular to thatplane. Thus, a lighting F number can be smaller than that in aconventional configuration, so that light diverging at larger anglesalso can be utilized. Therefore, a light source having a largerlight-emitting portion can be used, which improves the efficiency ofcondensing light from the light source, resulting in high-brightnessprojection images and a highly efficient system. Also, the size of anexit pupil in the direction parallel to the plane formed by the lightincident on and reflected from the reflection-type light valve isreduced, which allows the system size in that direction to be small.

In the first configuration, a reflection-type light valve that cancontrol the polarization directions of the incident light individuallyfor each pixel may be used as the reflection-type light valve describedabove. Moreover, a polarizer may be provided on an optical axis on theincident side of the reflection-type light valve and an analyzer may beprovided on an optical axis on the exit side thereof. Alternatively, areflection-type light valve provided with reflecting surfaces whoseinclination angle can be controlled individually for each pixel may beused as the reflection-type light valve described above. Moreover, thereflection-type light valve may display an image in such a manner thatthe inclination angle of the respective reflecting surfaces iscontrolled so as to change the emission angle of light, and therebylight to be incident on the projection optical system is selected foreach pixel.

Furthermore, a second configuration of a projection display system ofthe present second invention includes: a light source; a lightingoptical system for condensing the light from the light source on thedesired position; a reflection-type light valve provided with reflectingsurfaces whose inclination angle can be controlled individually for eachpixel and modulating the light from the lighting optical system bycontrolling the inclination angle of the respective reflecting surfaces,and a projection optical system for magnifying and projecting a pixel onthe reflection-type light valve. A schlieren optical system includingschlieren bars and a schlieren lens is arranged between the lightingoptical system and the reflection-type light valve. The shape of an exitpupil formed in the lighting optical system, which can be taken as alight-emitting surface when the lighting optical system is viewed fromthe schlieren bars, is such that the size in the direction parallel to aplane containing the axes of the light incident on and reflected fromthe reflection-type light valve is smaller than that in the directionperpendicular to that plane. Moreover, sin⁻¹(F4/2) and θ2/2+sin⁻¹(F3/2)are substantially equal, where, among a lighting F number relative tothe schlieren bars, F3 represents the lighting F number in the directionparallel to the plane containing the axes of the light incident on andreflected from the reflection-type light valve, F4 represents thelighting F number in the direction perpendicular to that plane, and θ2represents the angle between the light incident on the reflection-typelight valve and the light reflected from the reflection-type light valveinto the projection optical system.

In this configuration, the appearance of a light-emitting portion in thelighting optical system when viewed from the schlieren bars is optimizedin two directions; one is parallel to a plane formed by the lightincident on and reflected from the reflection-type light valve and theother is perpendicular to that plane. Thus, a lighting F number can besmaller than that in a conventional configuration, so that lightdiverging at larger angles also can be utilized. Therefore, a lightsource having a larger light-emitting portion can be used, whichimproves the efficiency of condensing light from the light source,resulting in high-brightness projection images and a highly efficientsystem. Also, the size of an exit pupil in the direction parallel to theplane formed by the light incident on and reflected from thereflection-type light valve is reduced, which allows the system size inthat direction to be small. On the other hand, a small-sized generallens can be used as a schlieren lens, so that an increase in the costcan be minimized.

In the first and second configuration, it is preferable that thelighting optical system is an integrated optical system including afirst lens array that divides the light from the light source intoseparate rays of light to form secondary images of the light source anda second lens array provided with a plurality of microlenses arranged atthe positions where the secondary images of the light source are formed;the entire shape of the second lens array is such that the size in thedirection parallel to a plane containing the axes of the light incidenton and reflected from the reflection-type light valve is smaller thanthat in the direction perpendicular to that plane. The use of theintegrated optical system in the lighting optical system allows for theimprovement of utilization efficiency of the light from the light sourceand the uniform luminance distribution in a projection image. Inaddition, the second lens array has the entire shape as described above,which can increase efficiency, brightness, and the degree of freedom inthe system structure.

BRIEF DESCRIPTION OF DRAWINGS

FIG. 1 shows a schematic configuration of a projection display system ofEmbodiment I-1 of the present first invention.

FIG. 2 is a front view showing a configuration of a color wheel used ina projection display system of the present first invention.

FIG. 3 is a perspective view showing a part of an optical system of aprojection display system of Embodiment I-1 of the present firstinvention.

FIG. 4 is a plan view showing a schematic configuration of a projectiondisplay system of Embodiment I-2 of the present first invention.

FIG. 5 is a side view showing a schematic configuration of a projectiondisplay system of Embodiment I-2 of the present first invention.

FIG. 6 is a perspective view showing a part of an optical system of aprojection display system of Embodiment I-2 of the present firstinvention.

FIG. 7 shows a configuration of a conventional lighting optical systemusing a rotating color wheel.

FIG. 8 shows a configuration of a conventional projection display systemusing a single-plate light valve operated by time-division driving.

FIG. 9 shows a schematic configuration of a projection display system ofEmbodiment II-1 of the present second invention.

FIG. 10 is a perspective view showing a part of an optical system of aprojection display system of Embodiment II-1 of the present secondinvention.

FIG. 11 is a view to assist in explaining the effect of a specialaperture stop of Embodiment II-1.

FIG. 12 shows a schematic configuration of a projection display systemof Embodiment II-1, when an integrated optical system is used in alighting optical system.

FIG. 13 is an external view showing a second lens array of EmbodimentII-1.

FIG. 14 is an external view showing another example of a second lensarray of Embodiment II-1.

FIG. 15 is an external view showing yet another example of a second lensarray of Embodiment II-1.

FIG. 16 is an external view showing yet another example of a second lensarray of Embodiment II-1.

FIG. 17 shows a schematic configuration of a projection display systemof Embodiment II-2 of the present second invention.

FIG. 18 is an external view showing a second lens array of EmbodimentII-2.

FIG. 19 shows a schematic configuration of a conventional projectiondisplay system using a reflection-type liquid crystal panel.

FIG. 20 shows a schematic configuration of a conventional projectiondisplay system using a reflection-type light valve.

FIG. 21 shows a schematic configuration of another example of aconventional projection display system using a reflection-type lightvalve.

DETAILED DESCRIPTION OF THE INVENTION First Invention

Embodiment I-1

FIG. 1 shows a schematic configuration of a projection display system100 of Embodiment I-1. The projection display system 100 of thisembodiment is provided with a first light source 102 on the optical axis101 of a first lamp, a first elliptical mirror 103, a second lightsource 105 on the optical axis 104 of a second lamp, and a secondelliptical mirror 106. The first elliptical mirror 103 has a reflectingsurface in the basic form that is rotationally symmetrical with respectto the optical axis 101. Similarly, the second elliptical mirror 106 hasa reflecting surface in the basic form that is rotationally symmetricalwith respect to the optical axis 104. Each of the first and the secondelliptical mirror has two focal points: The first light source 102 islocated at one focal point of the first elliptical mirror 103, and thesecond light source 105 is located at one focal point of the secondelliptical mirror 106; the two elliptical mirrors 103, 106 are arrangedso that the optical axis 101 and the optical axis 104 intersect at theother focal points of the elliptical mirrors, which are different fromthe focal points where the light sources are placed. Moreover, the twoelliptical mirrors 103, 106 are adjacent to each other with a systemaxis 107 sandwiched therebetween and arranged so that the distancebetween the light beams traveling through the outermost side in thedirection where the elliptical mirrors are close to each other isminimized.

As shown in FIG. 1, a color wheel 108 is arranged so that a color filterportion 109 of the color wheel 108 is located at the intersection of theoptical axes 101 and 104. The color wheel 108 is a disk having thering-shaped color filter portion 109, as shown in FIG. 2. The colorfilter portion 109 is divided into three parts at substantially equalangles: a blue-transmission dichroic filter 109 a, a green-transmissiondichroic filter 109 b, and a red-transmission dichroic filter 109 c. Thecolor wheel 108 is supported by a motor 110 at the center of thering-shaped color filter portion 109 and rotated at high speed.

The light from the light sources 102, 105 passes through the colorfilter portion 109 and is collimated into substantially parallel lightby passing through condenser lenses 111, 112. Then, the light passesthrough a filter 113 for rejecting ultraviolet and infrared rays andenters an integrated optical system 114.

FIG. 3 shows a perspective view showing the optical system between theintegrated optical system 114 and an analyzer 122, which will bedescribed later. In FIG. 3, the arrow along the system axis 107indicates the traveling direction of the light from the light sources.The description of a condenser lens 117 is omitted in FIG. 3.

The integrated optical system 114 includes a first lens array 115, asecond lens array 116, and the condenser lens 117. The first lens array115 is provided with many microlenses 119 arranged on the same plane.Each microlens 119 has an aperture that is similar in shape to theeffective portion of a transmission-type liquid crystal panel 118, whichwill be described later. Similarly, the second lens array 116 isprovided with many microlenses 120 arranged closely together on the sameplane. The microlenses 120 of the second lens array 116 are arranged atthe positions where secondary images of the light source are formed byeach microlens 119 of the first lens array 115. Each microlens 120magnifies the aperture shape of the corresponding microlens 119 of thefirst lens array 115 and projects it onto the transmission-type liquidcrystal panel 118. As a result, the images of the microlenses 119 of thefirst lens array 115 are superimposed to illuminate thetransmission-type liquid crystal panel 118 uniformly. Here, manymicrolenses 120 are arranged closely together so that the external shapeof the second lens array 116 when viewed from the transmission-typeliquid crystal panel 118 is substantially symmetrical with respect tothe system axis 107, as shown in FIG. 3. At this time, each microlens119 of the first lens array 115 is set so as to form the secondary imageof the light source on the corresponding microlens 120 of the secondlens array 116.

The light through the integrated optical system 114 enters a polarizer121, where the polarized component of the light parallel to thelight-absorption axis of the polarizer 121 is absorbed, so that onlylight having the polarized component perpendicular to that axis istransmitted and enters the transmission-type liquid crystal panel 118.

The transmission-type liquid crystal panel 118 is composed of manypixels that can modulate light individually in response to the inputsignals from the outside. Among the light incident on thetransmission-type liquid crystal panel 118, the polarization directionof the light entering a pixel to display black on a screen is changed by90 degrees when the light passes through the transmission-type liquidcrystal panel 118. Thus, the light is absorbed by an analyzer 122. Onthe other hand, the polarization direction of the light entering a pixelto display white on a screen is unchanged when the light passes throughthe transmission-type liquid crystal panel 118. Thus, the light istransmitted through the analyzer 122 and enters a projection lens 123,which is a projection optical system. As a result, an image on thetransmission-type liquid crystal panel 118 is magnified and projectedonto a screen 124.

In this embodiment, it should go without saying that the driving timingfor video signals is synchronized with the color of the light passingthrough the color wheel 108. Those video signals are input to thetransmission-type liquid crystal panel 118, corresponding to the RGBcolors.

With a conventional configuration merely employing two light sources(e.g., JP 6-242397 A and JP 6-265887 A), images of the light sources arelarge. However, the present embodiment can minimize the size of theimages of the light sources by optimizing the arrangement of two lightsources and superimposing two light source images formed on the rotatingcolor wheel 108 or its vicinity. Thus, the rotating color wheel 108 canhave the smallest diameter. This can provide high-brightness projectionimages because of a twofold increase in the light from the lightsources, while reducing the size of the set, the cost, and noise duringrotation, increasing reliability during rotation, and preventing colormixture.

In the above embodiment, the light from the light sources 102, 105 iscondensed by the elliptical mirrors 103, 106. However, the presentinvention is not limited thereto. For example, the same object can beattained with the following configuration: parabolic mirrors are usedinstead of the elliptical mirrors 103, 106; the light sources are placedat the focal positions of the parabolic mirrors, from which light isemitted as parallel light and condensed by a convex lens or the like.

In the above embodiment, the integrated optical system is used. However,when restrictions on the cost or the like have priority over imagequality, such an optical system is not necessarily needed, and theoptical system may consist of, e.g., a condenser lens.

In the above embodiment, the transmission-type liquid crystal panel 118is used as a light valve. However, the present invention is not limitedthereto. It should go without saying that other configurations may beemployed as long as the display system can modulate the input light inresponse to signals from the outside.

In a configuration of this embodiment, the angle of incidence of thelight entering the color wheel 108 is larger than that in the systemusing a single light source. When an increase in the angle of incidencecauses problems in practical use, the ends of the openings of theelliptical mirrors 103, 106, acting as reflectors of the light sources,may be cut away on the side where two mirrors are adjacent. Thus, thelight sources 102, 105 are close together, so that the angle ofincidence can be reduced.

The problem of red light can be improved by placing a bandpass filternear the filter 113 for rejecting ultraviolet and infrared rays of thisembodiment. The bandpass filter rejects only the yellow component.

As described above, this embodiment provides a projection display systemincluding: the light sources 102, 105; condensers (the ellipticalmirrors 103, 106) for condensing the light from the light sources; atime-division color separating optical system (the color wheel 108) fortemporally switching the incident light to a first, second, or thirdcolor of light to be emitted; a light valve (the transmission-typeliquid crystal panel 118) capable of modulating the incident lightindividually for each pixel; a lighting optical system (the condenserlenses 111, 112 and the integrated optical system 114) for directing thelight from the time-division color separating optical system onto thelight valve, and a projection optical system (the projection lens 123)for magnifying and projecting a pixel on the light valve. In such aprojection display system, the number of the light sources and thecondensers is two, respectively. The light from each of the lightsources is condensed on the time-division color separating opticalsystem or its vicinity by the condensers. Both condensing positions aresuperimposed. In addition, the two condensers are close togetheroptically. This can provide a projection display system that enableshigh brightness, low cost, and miniaturization.

Here, it is most preferable that the position, at which the images ofthe light sources condensed respectively by the two condensers aresuperimposed, is on the time-division color separating optical system(the color wheel 108). However, the position of the superimposition canbe shifted somewhat in the direction of the optical axis (the systemaxis 107) when it can be permissible in terms of the size of the colorwheel and that of the light source images.

In the case where the two elliptical mirrors 103, 106 that act ascondensers cannot be close together as shown in FIG. 1 because of therestrictions on structure and reliability, a general optical means maybe employed to ensure the structural distance between the ellipticalmirrors 103 and 106. Such an optical means includes placing a reflectingmirror on the incident side of the time-division color separatingoptical system (the color wheel 108), placing an optical path changingprism, and the like. At the same time, this makes it possible tooptically minimize the ineffective area of light between the twocondensers, when viewed from the time-division color separating opticalsystem (the color wheel 108).

Embodiment I-2

FIG. 4 is a top view showing a schematic configuration of a projectiondisplay system 200 of Embodiment I-2; FIG. 5 is a side view showing aschematic configuration (between a light source and a light valve) ofthe projection display system 200 of Embodiment I-2. The projectiondisplay system 200 of this embodiment is provided with a first lightsource 202 on the optical axis 201 of a first lamp, a first ellipticalmirror 203, a second light source 205 on the optical axis 204 of asecond lamp, and a second elliptical mirror 206. The first ellipticalmirror 203 has a reflecting surface in the basic form that isrotationally symmetrical with respect to the optical axis 201.Similarly, the second elliptical mirror 206 has a reflecting surface inthe basic form that is rotationally symmetrical with respect to theoptical axis 204. Each of the first and the second elliptical mirror hastwo focal points: The first light source 202 is located at one focalpoint of the first elliptical mirror 203, and the second light source205 is located at one focal point of the second elliptical mirror 206;the two elliptical mirrors 203, 206 are arranged so that the opticalaxis 201 and the optical axis 204 intersect at the other focal points ofthe elliptical mirrors, which are different from the focal points wherethe light sources are placed. Furthermore, the two elliptical mirrors203, 206 are adjacent to each other with a system axis 207 sandwichedtherebetween and arranged so that the distance between the light beamstraveling through the outermost side in the direction where theelliptical mirrors are close to each other is minimized.

As shown in FIGS. 4 and 5, a color wheel 208 is arranged so that a colorfilter portion 209 of the color wheel 208 is located at the intersectionof the optical axes 201 and 204. The color wheel 208 is a disk havingthe ring-shaped color filter portion 209, as shown in FIG. 2. The colorfilter portion 209 is divided into three parts at substantially equalangles: a blue-transmission dichroic filter 209 a, a green-transmissiondichroic filter 209 b, and a red-transmission dichroic filter 209 c. Thecolor wheel 208 is supported by a motor 210 at the center of thering-shaped color filter portion 209 and rotated at high speed.

The light from the light sources 202, 205 passes through the colorfilter portion 209 and is collimated into substantially parallel lightby passing through condenser lenses 211, 212. Then, the light passesthrough a filter 213 for rejecting ultraviolet and infrared rays andenters an integrated optical system 214.

The integrated optical system 214 includes a first lens array 215, asecond lens array 216, and a condenser lens 217. The first lens array215 is provided with many microlenses 219 arranged on the same plane.Each microlens 219 has an aperture that is similar in shape to theeffective portion of a reflection-type liquid crystal panel 218, whichwill be described later. Similarly, the second lens array 216 isprovided with many microlenses 220 arranged closely together on the sameplane. The microlenses 220 of the second lens array 216 are arranged atthe positions where secondary images of the light source are formed byeach microlens 219 of the first lens array 215. Each microlens 220magnifies the aperture shape of the corresponding microlens 219 of thefirst lens array 215 and projects it onto the reflection-type liquidcrystal panel 218. As a result, the images of the microlenses 219 of thefirst lens array 215 are superimposed to illuminate the reflection-typeliquid crystal panel 218 uniformly.

FIG. 6 is a perspective view showing the arrangement of the first lensarray 215, the second lens array 216, and the reflection-type liquidcrystal panel 218. In FIG. 6, the arrow along the system axis 207indicates the traveling direction of the light from the light sources.Unlike Embodiment I-1, many microlenses 220 are arranged closelytogether so that the external shape of the second lens array 216 whenviewed from the reflection-type liquid crystal panel 218 is limited inone direction (the direction 216 a), as shown in FIG. 6. Specifically,the external shape of the second lens array 216 is such that the size inthe direction 216 a is smaller than that in the direction 216 b, whichis perpendicular to the direction 216 a. The direction 216 a, in whichthe height of the second lens array 216 is limited, is parallel to aplane containing the axes of the light incident on and reflected fromthe effective portion of the reflection-type liquid crystal panel 218,which will be described later. In other words, the direction 216 a isincluded in that plane. Also, each microlens 219 of the first lens array215 is set so as to form the secondary image of the light source on thecorresponding microlens 220 of the second lens array 216.

The light through the integrated optical system 214 enters a polarizer221, where the polarized component of the light parallel to thelight-absorption axis of the polarizer 221 is absorbed, so that onlylight having the polarized component perpendicular to that axis istransmitted and enters the reflection-type liquid crystal panel 218.

The reflection-type liquid crystal panel 218 is composed of many pixelsthat can modulate light individually in response to the input signalsfrom the outside. Among the light incident on the reflection-type liquidcrystal panel 218, the polarization direction of the light entering apixel to display black on a screen is changed by 90 degrees when thelight reflects off the reflection-type liquid crystal panel 218. Thus,the light is absorbed by an analyzer 222. On the other hand, thepolarization direction of the light entering a pixel to display white ona screen is unchanged when the light reflects off the reflection-typeliquid crystal panel 218. Thus, the light is transmitted through theanalyzer 222. Here, the angle between the axes of the light incident onand reflected from the reflection-type liquid crystal panel 218 is θ1.

The light through the analyzer 222 enters a projection lens 223, whichis a projection optical system. As a result, an image on thereflection-type liquid crystal panel 218 is magnified and projected ontoa screen 224. At this time, the optical axis of the light reflected fromthe reflection-type liquid crystal panel 218 and the optical axis 223 aof the projection lens 223 are shifted, as shown in FIG. 4. Therefore,the light emitted from the projection lens 223 is projected onto thescreen to form a magnified image on the side opposed to thereflection-type liquid crystal panel 218 with respect to the opticalaxis 223 a of the projection lens 223 (i.e., the axis-shiftingprojection).

Here, as shown in FIG. 6, the shape of the second lens array 216 is setso as to satisfy F1>F2, where, among a lighting F number relative to thereflection-type liquid crystal panel 218, F1 represents the lighting Fnumber in the direction parallel to a plane (the direction 216 a)containing the axes of the light incident on and reflected from theeffective portion of the reflection-type liquid crystal panel 218; F2represents the lighting F number in the direction 216 b perpendicular tothat plane. Furthermore, the following relationship is established:

F1>1/(2 sin(θ1/2))

 F2<1/(2 sin(θ1/2))

where θ1 represents the angle between the light incident on thereflection-type liquid crystal panel 218 and the light reflected fromthe reflection-type liquid crystal panel 218 into the projection lens223.

In this embodiment, it should go without saying that the driving timingfor video signals is synchronized with the color of the light passingthrough the color wheel 208. Those video signals are input to thereflection-type liquid crystal panel 218, corresponding to the RGBcolors.

Like Embodiment I-1, with a conventional configuration merely employingtwo light sources (e.g., JP 6-242397 A and JP 6-265887 A), images of thelight sources are large. However, the present embodiment can minimizethe size of the images of the light sources by optimizing thearrangement of two light sources and superimposing two light sourceimages formed on the rotating color wheel 208 or its vicinity. Thus, therotating color wheel 208 can have the smallest diameter. This canprovide high-brightness projection images because of an twofold increasein the light from the light sources, while reducing the size of the set,the cost, and noise during rotation, increasing reliability duringrotation, and preventing color mixture.

In the above embodiment, the light from the light sources 202, 205 iscondensed by the elliptical mirrors 203, 206. However, the presentinvention is not limited thereto. For example, the same object can beattained with the following configuration: parabolic mirrors are usedinstead of the elliptical mirrors 203, 206; the light sources are placedat the focal positions of the parabolic mirrors, from which light isemitted as parallel light and condensed by a convex lens or the like.

In the above embodiment, the integrated optical system is used. However,when restrictions on the cost or the like have priority over imagequality, such an optical system is not necessarily needed, and theoptical system may consist of, e.g., a condenser lens.

In the above embodiment, the reflection-type liquid crystal panel 218 isused as a light valve. However, the present invention is not limitedthereto. It should go without saying that other configurations may beemployed as long as the display system can modulate the input light inresponse to signals from the outside.

Furthermore, instead of the reflection-type liquid crystal panel 218that controls the polarization directions of the incident light for eachpixel and reflects it, a small mirror array device also can be used,which is described in SID (ASIA DISPLAY '95), pp. 95-98. The smallmirror array device is provided with many rows of reflecting surfacescorresponding to each pixel. By controlling the reflecting surfaces tochange the inclination individually, the traveling direction of thereflected light can be changed. In this case, the above description canbe applied to the small mirror array device by replacing θ1, the anglebetween the light incident on and reflected from the reflection-typeliquid crystal panel 218 shown in FIGS. 4 and 6, with the angle betweenthe light entering the projection optical system 223 to form aprojection image among the reflected light and the incident light.

Also, it is obvious to those skilled in the art that the same idea canbe applied to the configuration, in which, though lighting efficiency issomewhat reduced, the integrated optical system is composed of acondenser lens and a special aperture stop; the special aperture stophas an aperture equal to the external shape of the second lens array 216described above.

In Embodiment I-2, the angle of incidence of the light entering thecolor wheel 208 is larger than that in the system using a single lightsource. When an increase in the angle of incidence causes problems inpractical use, the ends of the openings of the elliptical mirrors 203,206, acting as reflectors of the light sources, may be cut away on theside where two mirrors are adjacent. Thus, the light sources 202, 205are close together, so that the angle of incidence can be reduced.

The problem of red light can be improved by placing a bandpass filternear the filter 213 for rejecting ultraviolet and infrared rays of thisembodiment. The bandpass filter rejects only the yellow component.

As described above, this embodiment provides a projection display systemincluding: the light sources 202, 205; condensers (the ellipticalmirrors 203, 206) for condensing the light from the light sources; atime-division color separating optical system (the color wheel 208) fortemporally switching the incident light to a first, second, or thirdcolor of light to be emitted; a light valve (the reflection-type liquidcrystal panel 218) capable of modulating the incident light individuallyfor each pixel; a lighting optical system (the condenser lenses 211, 212and the integrated optical system 214) for directing the light from thetime-division color separating optical system onto the light valve, anda projection optical system (the projection lens 223) for magnifying andprojecting a pixel on the light valve. In such a projection displaysystem, the number of the light sources and the condensers is two,respectively. The light from each of the light sources is condensed onthe time-division color separating optical system or its vicinity by thecondensers. Both condensing positions are superimposed. In addition, thetwo condensers are close together optically. This can provide aprojection display system that enables high brightness, low cost, andminiaturization.

Here, it is most preferable that the position, at which the images ofthe light sources condensed respectively by the two condensers aresuperimposed, is on the time-division color separating optical system(the color wheel 208). However, the position of the superimposition canbe shifted somewhat in the direction of the optical axis (the systemaxis 207) when it can be permissible in terms of the size of the colorwheel or that of the light source images.

In the case where the two elliptical mirrors 203, 206 that act ascondensers cannot be close together as shown in FIG. 5 because of therestrictions on structure and reliability, a general optical means maybe employed to ensure the structural distance between the ellipticalmirrors 203 and 206. Such an optical means includes placing a reflectingmirror on the incident side of the time-division color separatingoptical system (the color wheel 208), placing an optical path changingprism, and the like. At the same time, this makes it possible tooptically minimize the ineffective area of light between the twocondensers, when viewed from the time-division color separating opticalsystem (the color wheel 208).

Furthermore, in Embodiment I-2, the plane containing the system axis207, the optical axis 201 of the first lamp, and the optical axis 204 ofthe second lamp is parallel to the vertical direction; of course, it maybe parallel to the horizontal direction.

Second Invention

Embodiment II-1

FIG. 9 shows a schematic configuration of a projection display system ofEmbodiment II-1. FIG. 10 is a perspective view showing a part of anoptical system of a projection display system of Embodiment II-1.

In a projection display system 500 of this embodiment, the light from alight source 501 is emitted by a reflector 502 along a system axis 520.Then, the light enters a condenser lens 504 that constitutes a lightingoptical system 503. The light through the condenser lens 504 passesthrough a special aperture stop 505, and diagonally enters a panel unit506 at the angle of incidence of θ1/2, as shown in FIG. 9.

The panel unit 506 includes a reflection-type liquid crystal panel 507and a polarizing plate 508. The reflection-type liquid crystal panel 507is composed of many pixels that can modulate light individually inresponse to the input signals from the outside. The polarizing plate 508is provided in proximity to the reflection-type liquid crystal panel 507on its incident side and acts as a polarizer as well as an analyzer.Natural light enters the panel unit 506, where the polarized componentof the light parallel to the light-absorption axis of the polarizingplate 508 is absorbed, so that only light having the polarized componentperpendicular to that axis is transmitted and enters the reflection-typeliquid crystal panel 507. Among the light entering here, thepolarization direction of the light entering a pixel to display black ona screen is changed by 90 degrees when the light reflects off thereflection-type liquid crystal panel 507. Thus, the light is absorbed bythe polarizing plate 508, which acts as an analyzer. On the other hand,the polarization direction of the light entering a pixel to displaywhite on a screen is unchanged when the light reflects off thereflection-type liquid crystal panel 507. Thus, the light is transmittedthrough the polarizing plate 508, which acts as an analyzer. Here, theangle between the light incident on the reflection-type liquid crystalpanel 507 and the light reflected from the reflection-type liquidcrystal panel 507 through the polarizing plate 508 is θ1.

The light reflected from the reflection-type liquid crystal panel 507passes through the polarizing plate 508 and enters a projection lens509, which is a projection optical system. As a result, an image on thereflection-type liquid crystal panel 507 is magnified and projected ontoa screen 510. At this time, the optical axis of the light reflected fromthe reflection-type liquid crystal panel 507 and the optical axis 509 aof the projection lens 509 are shifted, as shown in FIG. 9. Therefore,the light emitted from the projection lens 509 is projected onto thescreen to form a magnified image on the side opposed to thereflection-type liquid crystal panel 507 with respect to the opticalaxis 509 a of the projection lens 509 (i.e., the axis-shiftingprojection).

Here, as shown in FIG. 10, the shape of an aperture 505 c in the specialaperture stop 505 is set so as to satisfy F1>F2, where, among a lightingF number relative to the reflection-type liquid crystal panel 507, F1represents the lighting F number in the direction parallel to a plane(the direction 505 a) containing the axes of the light incident on andreflected from the effective portion of the reflection-type liquidcrystal panel 507; F2 represents the lighting F number in the direction505 b perpendicular to that plane. Furthermore, the followingrelationship is established:

F1>1/(2 sin (θ1/2))

F2<1/(2 sin (θ1/2))

where θ1 represents the angle between the light incident on thereflection-type liquid crystal panel 507 and the light reflected fromthe reflection-type liquid crystal panel 507 into the projection lens509.

This configuration provides a simple structure without using a PBS,thereby increasing the degree of freedom in a light source setting.Thus, high efficiency and high brightness can be achieved.

F1 is determined by the following factors: the interference between thelighting optical system and the projection optical system; poor contrastcaused by an increase in the angle of incidence of the light enteringthe reflection-type liquid crystal panel 507, and the limitation on theamount of axis-shifting required for the position of projection.

On the other hand, F2 is determined by the F number of the projectionoptical system.

When F1=1/(2 sin(θ1/2)), the smallest parts of the light incident on andreflected from the reflection-type liquid crystal panel 507 aresuperimposed. Thus, F1>1/(2 sin(θ1/2)) has to be established.

In a conventional configuration, the lighting F number in the directionparallel to a plane containing the axes of the light incident on andreflected from the effective portion of the reflection-type liquidcrystal panel 507 is the same as the lighting F number in the directionperpendicular to that plane, i.e., both are represented by F1. In otherwords, an aperture in a stop is circular, having a diameter equal to anaperture width of the aperture stop 505 of this embodiment in the 505 adirection. Moreover, there is the lowest limit to F1, as describedabove. For these reasons, it is impossible to reduce the lightning Fnumber and improve the condensing efficiency.

On the other hand, in this embodiment, the use of the special aperturestop 505 increases the angle of divergence of the light entering theeffective portion of the reflection-type liquid crystal panel 507 in thedirection 505 b, i.e., F1>F2 is achieved. In other words, F2<1/(2sin(θ1/2)) is established.

Here, the extent of improvement of brightness according to thisembodiment is calculated by showing the specific values. For example,when θ1=20 degrees, F1>2.88 and F2<2.88 are given by the above twoinequalities. Therefore, as shown in FIG. 11, in the case where thespecial aperture stop 405 having, e.g., F1=3 and F2=2 is used, thisembodiment can provide brightness that is about 1.8 times that of aconventional configuration including a circular aperture stop of F1=3,assuming that the distribution of the light from the condenser lens 504is uniform. In FIG. 11, the reference numeral 505 c indicates theaperture shape of the special aperture stop 505 of this embodiment; thereference numeral 519 indicates the aperture shape of a conventionalcircular aperture stop.

In the above description, the lighting optical system 503 is composed ofthe condenser lens 504. However, the present invention is not limitedthereto. For example, the lighting optical system 503 may be composed ofan integrated optical system including a first lens array 512 and asecond lens array 513, as shown in FIG. 12.

The first lens array 512 is provided with many microlenses 514 arrangedon the same plane. Each microlens 514 has an aperture that is similar inshape to the effective portion of the reflection-type liquid crystalpanel 507. Similarly, the second lens array 513 is provided with manymicrolenses 515 arranged closely together on the same plane. Themicrolenses 515 of the second lens array 513 are arranged at thepositions where the secondary images of the light source are formed byeach microlens 514 of the first lens array 512. Each microlens 515magnifies the aperture shape of the corresponding microlens 514 of thefirst lens array 512 and projects it onto the reflection-type liquidcrystal panel 507. As a result, the images of the microlenses 514 of thefirst lens array 512 are superimposed to illuminate the reflection-typeliquid crystal panel 507 uniformly.

Here, as shown in FIG. 13, many microlenses 515 are arranged closelytogether so that the external shape of the second lens array 513 whenviewed from the reflection-type liquid crystal panel 507 is limited inone direction (the vertical direction of the sheet of the drawing).Specifically, the external shape of the second lens array 513 is suchthat the size in the vertical direction of the drawing sheet is smallerthan that in the lateral direction thereof. The direction (the verticaldirection of the drawing sheet), in which the height of the second lensarray 513 is limited, is parallel to a plane containing the axes of thelight incident on and reflected from the effective portion of thereflection-type liquid crystal panel 507. In other words, the verticaldirection of FIG. 13 is included in that plane. Also, each microlens 514of the first lens array 512 is set so as to form the secondary image ofthe light source on the corresponding microlens 515 of the second lensarray 513. In this case, the lighting F numbers are set in the samemanner as for the special aperture stop 505.

When the special aperture stop 505 described above is used, a part ofthe light from the light source 501 is blocked by the stop, so that allthe light is not used effectively to project an image. However, the useof the optimized integrated optical system in this embodiment makes itpossible to set the shape of the emission portion of the lightingoptical system without causing losses. Thus, a system with high lightutilization efficiency can be provided.

In FIG. 13, the second lens array 513 has a substantially oval shape.However, the external shape of the second lens array 513 is not limitedthereto. For example, it can be rectangular as shown in FIG. 14,hexagonal as shown in FIG. 15, elliptical as shown in FIG. 16, or thelike.

In the above panel unit 506, in the case where the incident light isreflected without changing in its polarization direction, a whiteportion is displayed on a screen. However, other panels can be appliedto this embodiment, in which the polarization direction of the incidentlight is changed by 90 degrees when the light is reflected, and thus awhite portion is displayed on a screen. In this case, it is obvious thata polarizer and analyzer are composed preferably of separate polarizingplates, each having an axis extending in different directions; it shouldgo without saying that the present invention can be also applied tothis.

Embodiment II-2

FIG. 17 shows a schematic configuration of a projection display systemof Embodiment II-2. In a projection display system 600 of thisembodiment, the light from a light source 601 is emitted by a reflector602 along a subsystem axis 621. Then, the light enters a lightingoptical system 603. The lighting optical system 603 is composed of anintegrated optical system including a first lens array 604 and a secondlens array 608. The first lens array 604 is provided with manymicrolenses 605 arranged on the same plane. Each microlens 605 has anaperture that is similar in shape to the effective portion of areflection-type light valve 606, which will be described later. Inaddition, the aperture shape of the microlens 605 is designed so thatthe angle between the subsystem axis 621 and a system axis 620 is takeninto account to illuminate schlieren bars 607, which will be describedlater. Also, the second lens array 608 is provided with many microlenses609 arranged closely together on the same plane. The microlenses 609 ofthe second lens array 608 are arranged at the positions where secondaryimages of the light source are formed by each microlens 605 of the firstlens array 604.

Each microlens 609 magnifies the aperture shape of the correspondingmicrolens 605 of the first lens array 604 through a condenser lens 610and projects it onto the position of the schlieren bars 607. In otherwords, the light from the light source 601 is once divided by the firstlens array 604, and then superimposed at the position of the schlierenbars 607, where a third image of the light source is formed.

The light incident on the schlieren bars 607 is reflected therefrom,then enters a schlieren lens 611, and is focused to form an image on thereflection-type light valve 606 again.

The effective display area in the reflection-type light valve 606 isprovided with many reflecting surfaces (not shown) formed closelytogether. The inclination angle of the respective reflecting surfacescan be controlled individually for each pixel. Since the reflectingsurface of a pixel to display black on a screen is not inclined, thelight incident perpendicularly on this surface is reflected therefrom,retraces the same optical path, and forms an image on the schlieren bars607 again. Then, the light is reflected from the schlieren bars towardthe subsystem axis 621 and returns to the light source. Thus, the lightbeam does not reach a projection lens 612, which is a projection opticalsystem, resulting in a black portion in the projection image. On theother hand, since the reflecting surface of a pixel to display white ona screen is inclined at an angle of θ, the light incident on thissurface is reflected at an angle of 2θ with respect to the system axis620 and forms an image at the position of the schlieren bars 607 again,like the above. However, since the reflected light is inclined withrespect to the system axis 620, it does not form an image on theschlieren bars 607 and passes between the bars. The light thustransmitted through the schlieren bars 607 enters the projection lens612 and is projected onto a screen (not shown). In such a manner, theeffective display portion of the reflection-type light valve 606 isprojected to form a magnified image on a screen.

In the above configuration, an F number of the schlieren lens 611 on theside of the schlieren bars 607 has to be large enough to cover the angleof convergence required for illuminating the schlieren bars 607 with thelight from the light source 601 by the lighting optical system 603. Inaddition, to form an image on the schlieren bars 607 (more precisely,between the bars) again without causing light loss by focusing the lightreflected from the reflecting surface in the reflection-type light valve606, the surface being inclined at an angle of θ, it is necessary toreduce the F number on the side of the schlieren bars 607 by the amountcorresponding to the inclination angle 2θ of the light emitted from thelight valve 606.

Thus, in this embodiment, many microlenses 609 are arranged closelytogether so that the external shape of the second lens array 608 whenviewed from the subsystem axis 621 is limited in one direction (thevertical direction of the sheet of the drawing), as shown in FIG. 18.Specifically, the external shape of the second lens array 608 is suchthat the size in the vertical direction of the drawing sheet is smallerthan that in the lateral direction thereof. Of course, it should gowithout saying that each microlens 605 of the first lens array 604 isset so as to form the secondary image of the light source on thecorresponding microlens 609 of the second lens array. The direction (thevertical direction of the sheet of FIG. 18), in which the height of thesecond lens array 608 is limited, is parallel to a plane containing thesubsystem axis 621 and the system axis 620. In other words, thedirection is parallel to the plane containing the axis of the lightincident on the reflection-type light valve 606 from the schlieren lens611 and the axis of the light reflected from the reflection-type lightvalve 606.

Here, it is preferable that the following relationship is establishedsubstantially:

sin⁻¹(F4/2)=θ2/2+sin⁻¹(F3/2)

where, among a lighting F number relative to the schlieren bars 607, F3represents the lighting F number in the direction parallel to a planecontaining the axes of the light incident on and reflected from thereflection-type light valve 606; F4 represents the lighting F number inthe direction perpendicular to that plane, and θ2 represents the anglebetween the light incident on the reflection-type light valve 606 andthe light reflected from the reflection-type light valve 606 into theprojection lens 612.

The above equation means that, in the schlieren lens 611, the lighting Fnumber (the angle of divergence of light) in the direction parallel tothe plane containing the axes of the light incident on and reflectedfrom the reflection-type light valve 606 is the same as the lighting Fnumber in the direction perpendicular to that plane. When this equationis satisfied, the schlieren lens 611 can have the minimum size to berequired, even if a general lens with a circular pupil is used as theschlieren lens 611. Thus, the cost can be minimized.

Furthermore, since the second lens array 608 is formed generally bypressing or molding, the formation of the lens array into a shape thatis asymmetrical with respect to the optical axis as described above doesnot increase the cost by a significant amount. Thus, the brightnessperformance can be maintained.

Also, it is obvious to those skilled in the art that the same idea canbe applied to the configuration, in which, though lighting efficiency issomewhat reduced, the optical system 603 is composed of a condenser lensand a special aperture stop as described in Embodiment II-1.

The invention may be embodied in other forms without departing from thespirit or essential characteristics thereof. The embodiments disclosedin this application are to be considered in all respects as illustrativeand not limiting. The scope of the invention is indicated by theappended claims rather than by the foregoing description, and allchanges which come within the meaning and range of equivalency of theclaims are intended to be embraced therein.

What is claimed is:
 1. A projection display system comprising: a lightsource; a condenser for condensing light from the light source; atime-division color separating optical system for temporally switchingincident light to a plurality of different colors of light to beemitted; a light valve capable of modulating incident light individuallyfor each pixel; a lighting optical system for directing light from thetime-division color separating optical system onto the light valve, anda projection optical system for magnifying and projecting a pixel on thelight valve, wherein the number of the light source and the condenser isat least two, respectively, the light sources emitting lightsimultaneously, light from the light sources being condensed on thetime-division color separating optical system by the condensers, andboth condensing positions are superimposed.
 2. The projection displaysystem according to claim 1, wherein the condenser includes anumbrella-type reflector provided with an elliptical reflecting surface.3. The projection display system according to claim 1, wherein thecondenser includes an umbrella-type reflector provided with a parabolicreflecting surface and optical components having a convex-lens effect.4. The projection display system according to claim 1, wherein thelighting optical system includes a lens for collimating light from thetime-division color separating optical system into substantiallyparallel light and an integrated optical system, and the integratedoptical system includes a first lens array that divides incident lightinto separate rays of light to form secondary images of the light sourceand a second lens array provided with a plurality of microlensesarranged at the positions where the secondary images of the light sourceare formed.
 5. The projection display system according to claim 1,wherein the light valve is a reflection-type light valve.
 6. Theprojection display system according to claim 5, wherein a shape of anexit pupil formed in the lighting optical system, which can be taken asa light-emitting surface when the lighting optical system is viewed fromthe reflection-type light valve, is such that a size in a directionparallel to a plane containing axes of light incident on and reflectedfrom the reflection-type light valve is smaller than that in a directionperpendicular to that plane, and the following relationship isestablished: F1>1/(2 sin(θ1/2)) F2<1/(2 sin(θ1/2)) where, among alighting F number relative to the reflection-type light valve, F1represents the lighting F number in the direction parallel to the planecontaining the axes of the light incident on and reflected from thereflection-type light valve, F2 represents the lighting F number in thedirection perpendicular to that plane, and θ1 represents an anglebetween the light incident on the reflection-type light valve and thelight reflected from the reflection-type light valve into the projectionoptical system.
 7. The projection display system according to claim 5,wherein the reflection-type light valve can control polarizationdirections of incident light individually for each pixel, and apolarizer is provided on an optical axis on an incident side of thereflection-type light valve and an analyzer is provided on an opticalaxis on an exit side thereof.
 8. The projection display system accordingto claim 5, wherein the reflection-type light valve is provided withreflecting surfaces whose inclination angle can be controlledindividually for each pixel, and displays an image in such a manner thatthe inclination angle of the respective reflecting surfaces iscontrolled so as to change an emission angle of light, and thereby lightto be incident on the projection optical system is selected.
 9. Theprojection display system according to claim 5, wherein the lightingoptical system includes a lens for collimating light from thetime-division color separating optical system into substantiallyparallel light and an integrated optical system, the integrated opticalsystem includes a first lens array that divides incident light intoseparate rays of light to form secondary images of the light source anda second lens array provided with a plurality of microlenses arranged atthe positions where the secondary images of the light source are formed,and an entire shape of the second lens array is such that a size in adirection parallel to a plane containing axes of light incident on andreflected from the reflection-type light valve is smaller than that in adirection perpendicular to that plane.
 10. The projection display systemaccording to claim 5, wherein a plane containing a system axis and thetwo light sources is perpendicular to a plane containing axes of lightincident on and reflected from the reflection-type light valve.
 11. Theprojection display system according to claim 1, wherein thetime-division color separating optical system is a rotating color wheelhaving a light selecting means that is placed on a circumference of acircle whose center is the center of rotation of the color wheel andseparates incident white light into a plurality of different colors oflight to be emitted.
 12. A projection display system comprising: a lightsource; a lighting optical system for condensing light from the lightsource on a desired position; a reflection-type light valve capable ofmodulating light from the lighting optical system individually for eachpixel, and a projection optical system for magnifying and projecting apixel on the reflection-type light valve, wherein a shape of an exitpupil formed in the lighting optical system, which can be taken as alight-emitting surface when the lighting optical system is viewed fromthe reflection-type light valve, is such that a size in a directionparallel to a plane containing axes of light incident on and reflectedfrom the reflection-type light valve is smaller than that in a directionperpendicular to that plane, and the following relationship isestablished: F1>1/(2 sin(θ1/2)) F2<1/(2 sin(θ1/2)) where, among alighting F number relative to the reflection-type light valve, F1represents the lighting F number in the direction parallel to the planecontaining the axes of the light incident on and reflected from thereflection-type light valve, F2 represents the lighting F number in thedirection perpendicular to that plane, and θ1 represents an anglebetween the light incident on the reflection-type light valve and thelight reflected from the reflection-type light valve into the projectionoptical system.
 13. The projection display system according to claim 12,wherein the reflection-type light valve can control polarizationdirections of incident light individually for each pixel, and apolarizer is provided on an optical axis on an incident side of thereflection-type light valve and an analyzer is provided on an opticalaxis on an exit side thereof.
 14. The projection display systemaccording to claim 12, wherein the reflection-type light valve isprovided with reflecting surfaces whose inclination angle can becontrolled individually for each pixel, and displays an image in such amanner that the inclination angle of the respective reflecting surfacesis controlled so as to change an emission angle of light, thereby lightto be incident on the projection optical system is selected.
 15. Aprojection display system comprising: a light source; a lighting opticalsystem for condensing light from the light source on a desired position;a reflection-type light valve provided with reflecting surfaces whoseinclination angle can be controlled individually for each pixel andmodulating light from the lighting optical system by controlling theinclination angle of the respective reflecting surfaces, and aprojection optical system for magnifying and projecting a pixel on thereflection-type light valve, wherein a schlieren optical systemincluding schlieren bars and a schlieren lens is arranged between thelighting optical system and the reflection-type light valve, and a shapeof an exit pupil formed in the lighting optical system, which can betaken as a light-emitting surface when the lighting optical system isviewed from the schlieren bars, is such that a size in a directionparallel to a plane containing axes of light incident on and reflectedfrom the reflection-type light valve is smaller than that in a directionperpendicular to that plane, and sin⁻¹(F4/2) and θ2/2+sin⁻¹(F3/2) aresubstantially equal, where, among a lighting F number relative to theschlieren bars, F3 represents the lighting F number in the directionparallel to the plane containing the axes of the light incident on andreflected from the reflection-type light valve, F4 represents thelighting F number in the direction perpendicular to that plane, and θ2represents an angle between the light incident on the reflection-typelight valve and the light reflected from the reflection-type light valveinto the projection optical system.
 16. The projection display systemaccording to claim 12, wherein the lighting optical system is anintegrated optical system including a first lens array that divideslight from the light source into separate rays of light to formsecondary images of the light source and a second lens array providedwith a plurality of microlenses arranged at the positions where thesecondary images of the light source are formed, and an entire shape ofthe second lens array is such that a size in a direction parallel to aplane containing axes of light incident on and reflected from thereflection-type light valve is smaller than that in a directionperpendicular to that plane.
 17. The projection display system accordingto claim 15, wherein the lighting optical system is an integratedoptical system including a first lens array that divides light from thelight source into separate rays of light to form secondary images of thelight source and a second lens array provided with a plurality ofmicrolenses arranged at the positions where the secondary images of thelight source are formed, and an entire shape of the second lens array issuch that a size in a direction parallel to a plane containing axes oflight incident on and reflected from the reflection-type light valve issmaller than that in a direction perpendicular to that plane.